Campaign finance

FILE - In this May 16, 2019, file photo, Democratic presidential candidate Sen. Elizabeth Warren, D-Mass., addresses a campaign rally at George Mason University in Fairfax, Va. Democrats running for the White House rail against the flood of campaign cash that courses through the political system. But it’s becoming clear that those pledges often come with asterisks. Warren has vowed no untraceable “dark money” will help her, despite being backed by an organization that doesn’t disclose some of its donors.(AP Photo/Cliff Owen, File)

FILE - In this March 6, 2019 photo, Michael Cohen, President Donald Trump's former personal lawyer departs the Capitol in Washington. Prosecutors aren’t quite finished investigating campaign finance violations by Cohen. A federal judge in New York agreed Tuesday, May 21 to keep search warrant materials related to the investigation under seal until at least mid-July after prosecutors submitted a letter explaining that the probe is still ongoing. Cohen is serving a three-year prison sentence after admitting paying off two women who claimed they had affairs with Trump. (AP Photo/J. Scott Applewhite, File)

House Oversight and Reform National Security subcommittee member Rep. Justin Amash, R-Mich., looks out from the dais on Capitol Hill in Washington, Wednesday, May 22, 2019, during the House Oversight and Reform National Security subcommittee hearing on "Securing U.S. Election Infrastructure and Protecting Political Discourse." (AP Photo/Carolyn Kaster)

FILE - This Oct. 24, 2016, file photo shows dollar bills in New York. Almost the entire 2020 Democratic presidential field has joined the labor movement driven by fast food workers to implement a federal minimum wage of $15. (AP Photo/Mark Lennihan, File)

Democratic Progressive Party (DPP) supporters attend a final election rally led by Malawian President, Peter Mutharika, in Blantyre, Malawi Saturday, May 18, 2019. Corruption and the need for economic growth are the main campaign issues as Malawi goes to the polls on Tuesday for a presidential election that pits the incumbent 78-year-old president Peter Mutharika of the ruling Democratic Progressive Party against his own vice president, 46-year-old Saulos Chilima as well as the main opposition party leader Lazarus Chakwera, 64. (AP Photo/Thoko Chikondi)

FILE - In this Tuesday, May 7, 2019 file photo, State Sen. Dan Bishop answers a question during a debate among Republican candidates for the 9th congressional district in Monroe, N.C. Bishop on Tuesday, May 14, 2019, topped nine other GOP candidates seeking the 9th Congressional District nomination with almost half of the ballots cast. He will face Democrat Dan McCready, as well as Libertarian and Green candidates, on Sept. 10. (AP Photo/Chuck Burton, File)

FILE - In a Wednesday, May 1, 2019 file photo, Democratic presidential candidates Sen. Cory Booker, D-N.J., left, and Sen. Kamala Harris, D-Calif., center, listen as Attorney General William Barr testifies during a Senate Judiciary Committee hearing on Capitol Hill in Washington, on the Mueller Report. The Democrats who want to be president are swarming California, competing for campaign cash and media attention while courting longtime allies of home-state Sen. Kamala Harris on their rival’s own turf.(AP Photo/Andrew Harnik, File)

2020 Democratic presidential candidate Sen. Elizabeth Warren speaks to local residents during an organizing event, Friday, May 3, 2019, in Ames, Iowa.(AP Photo/Charlie Neibergall)

President Donald Trump arrives at a rally at Resch Center Complex in Green Bay, Wis., Saturday, April 27, 2019. (AP Photo/Andrew Harnik)